The invention relates generally to ultra high frequency radio wave generators and more specifically to generators operating at the top of this range, namely at a few dozen gigahertz, i.e. in the millimeter and submillimeter wave bands.
Several types of electron tubes for this use are known from the prior art. In one type, an electron beam advances along an axis where it is subject to the action of a uniform magnetic field, which is constant in time and directed along this axis, as well as to that of a high frequency electrical field directed transversely with respect to the field and whose frequency is equal to the cyclotron frequency of the electrons in the magnetic field in question.
In tubes of this type the electrons are produced by a device which inparts thereto a velocity component which is directed transversely to the axis. This device is generally an electron gun, whose cathode is in the form of a ring and produces a hollow cylindrical beam.
The high frequency electrical field comprises the electrical component of the electromagnetic field occurring within resonant cavities that are placed along the path of, and are coupled to, the beam.
Under these conditions the electrons travel along the axis in spiral paths and during the last part of their travel are able to transfer radio energy at the electromagnetic field frequency, or a multiple thereof, as a result of alternating high frequency components formed within the beam in the first part of the path. The radio energy produced at this frequency is collected in one or more loads coupled to the final resonant cavity.
In the prior art tubes the energy is supplied to the electrons solely by the direct current supply which accelerates them, there being no other energy source in the system.
Over the past few years developments have taken place in connection with this type of tube, and information on these is provided in the report by V. A. FLYAGIN, A. V. GAPONOV, M. I. PETELIN, V. K. JULPATOV "The Gyrotron" Second International Conference and Winter School on Submillimeter Waves and their Applications. Dec. 6-11, 1976--Puerto-Rico.
Thus, these tubes are characterised by the high values of the accelerating direct voltage applied to the beam in order to give the beam the desired high energy. They are also characterised by high intensity magnetic fields. It is known that the intensity of the magnetic field B and the cyclotron frequency f.sub.c (.omega..sub.c =2.pi.f.sub.c) are two proportional magnitudes: .omega..sub.c =eB/m.sub.o, e and m.sub.o representing respectively the charge and mass of the electron at rest.
However, the application of high direct voltages comes up against insulation difficulties in the case of these wavelengths where very small circuits are used. The application of the necessary magnetic fields generally leads to the use of superconducting circuits if the necessary values are to be reached, which exceed the maximum values attainable under normal conditions, but it is known that the construction and utilisation of such circuits are difficult.